const x7 = 1; 
let  x: number = 1; // 类型标注
const x2: number = 1;
// const x4 = 1;
let x5 = 1 as const; // 字面类型 类型断言
var x3:number = 1;
// let x4 ="a" as unknown as number;
let x6 = foo('a', false) as number;

function foo(s: string, b: boolean): number {
  return 1;
}

class MyClass {
  foo(): number {
    return 1;
  }
}

for (let index: number = 0 ...) 

try {
  
} catch (e: unknown) {

}

// import ..